The disclosure of Japanese Patent Application No. 2000-078134 filed on Mar. 21, 2000 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to a variable valve drive mechanism of an internal combustion engine capable of varying valve characteristics of intake valves or exhaust valves of the engine, and also relates to an intake air amount control apparatus of an internal combustion engine that employs the variable valve drive mechanism.
2. Description of Related Art
Variable valve drive mechanisms adapted to vary the amount of lift or the operating angle of intake valves or exhaust valves of an internal combustion engine in accordance with the operating state or conditions of the engine are known in the art. An example of such mechanisms is disclosed in Japanese laid-open Patent Publication (Kokai) No. 11-324625, in which a rocking cam is provided coaxially with a rotating cam that rotates or moves in accordance with a crankshaft, and the rotating cam and the rocking cam are connected to each other by a complicated link mechanism. The variable valve drive mechanism further includes a control shaft disposed midway in the complicated link mechanism. The phase of the rocking cam may be changed by causing the control shaft to displace or offset the center of rocking of an arm that forms a portion of the link mechanism. By changing the phase of the rocking cam in this manner, the amount of lift or the operating angle of the intake or exhaust valves can be varied. This makes it possible to improve the fuel economy and achieve stable operating characteristics of the engine during, for example, low-speed and low-load operations, and to improve the intake air charging efficiency to thereby ensure sufficiently large outputs during, for example, high-speed and high-load operations.
However, the link mechanism, which links the rotating cam and the rocking cam that are disposed on the same axis, is likely to be long and complicated. This may result in reduced certainty or reliability in the operations of the variable valve drive mechanism.
It is therefore an object of the invention to provide a variable valve drive mechanism of an internal combustion engine that operates with sufficient certainty or reliability, without requiring a long and complicated link mechanism as employed in the conventional engine. It is another object of the invention to provide an intake air amount control apparatus that utilizes the variable valve drive mechanism.
To accomplish the above object and/or other object(s), a first aspect of the invention provides a variable valve drive mechanism of an internal combustion engine, which is capable of varying a valve characteristic of an intake valve or an exhaust valve of the internal combustion engine, comprising: (a) a camshaft that is operatively connected with a crankshaft of the engine such that the camshaft is rotated by the crankshaft; (b) a rotating cam provided on the camshaft; (c) an intermediate drive mechanism disposed between the camshaft and the valve and supported rockably on a shaft that is different from the camshaft, the intermediate drive mechanism including an input portion operable to be driven by the rotating cam of the camshaft, and an output portion operable to drive the valve when the input portion is driven by the rotating cam; and (d) an intermediate phase-difference varying device positioned and configured to vary a relative phase difference between the input portion and the output portion of the intermediate drive mechanism.
The intermediate drive mechanism having the input portion adapted to be driven by the rotating cam and the output portion that drives the valve when the input portion is driven by the rotating cam is rockably supported by the shaft that is different from the camshaft on which the rotating cam is provided. With this arrangement, there is no need to provide a long, complicated link mechanism for connecting the rotating cam with the intermediate drive mechanism (or rocking cam). Thus, when the rotating cam drives the input portion of the intermediate drive mechanism, the driving force is readily transmitted from the input portion to the output portion within the drive mechanism, so that the output portion drives the intake or exhaust valve in accordance with the driving state of the rotating cam.
The intermediate phase-difference varying device is capable of varying a relative phase difference between the input and output portions of the intermediate drive mechanism. It is thus possible to advance or retard the start of lifting of the intake or exhaust valve that occurs in accordance with the driving state (or rotational phase) of the rotating cam, thus making it possible to adjust the amount of lift or operating angle of the valve that varies with the driving state or rotational phase of the rotating cam.
As described above, the amount of lift or operating angle of the intake or exhaust valve may be changed with a relatively simple construction in which the relative phase difference between the input and output portions is changed, without requiring the conventional long and complicated link mechanism. It is thus possible to provide a variable valve drive mechanism of an internal combustion engine that operates with improved certainty and reliability.
In one preferred embodiment of the invention, the output portion comprises a rocking cam that includes a nose, and the intermediate phase-difference varying device is operable to vary the relative phase difference between the nose of the rocking cam and the input portion.
In the above-described variable valve drive mechanism in which the output portion principally consists of the rocking cam, the intermediate phase-difference varying device is able to vary the relative phase difference between the nose formed on the rocking cam and the input portion, thereby to advance or retard (or delay) the start of lifting of the intake or exhaust valve that occurs in accordance with the driving state (or rotational phase) of the rotating cam provided on the camshaft. Since the amount of lift or operating angle of the intake or exhaust valve can be varied with such a simple construction, the variable valve drive mechanism can operate with improved certainty and reliability.